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-   -   Metal halide ballasts breaking prematurely (https://www.diychatroom.com/f18/metal-halide-ballasts-breaking-prematurely-85714/)

BluesBpy721 11-03-2010 08:45 PM

Metal halide ballasts breaking prematurely
 
So I have an interesting situation. At the apartment complex I work at, I replaced 20 year old high pressure sodium fixtures with 70w metal halide ballasts a year ago. Here's the situation:

Within a few months, 6 of these ballasts toasted. As well as 4 bulbs burning out. I had these fixtures picked up under warranty and got all of them installed. Within the week of checking all of the fixtures and getting them installed, one more toasted (this time the ballast looks unharmed). Also, one of the new fixtures I installed broke within a few hours and once again...the ballast looked clean, unlike the 6 that fried actually looked like they burnt up.

I was wondering if any of you have any idea what's going on here. These are not supposed to break within a few months and the light bulbs are supposed to last. These fixtures are installed on a photocell circuit at 15A/120V.

Oh and also, most buildings has 2 of these installed on each corner of the back. I've noticed on 5 separate buildings in which only one fixture toasted while the opposite fixture is absolutely fine. I've actually had a building where I replaced the broken one and within 2 weeks of it being installed the opposite fixture broke.

I was thinking that the circuit is overwhelmed somehow. We have 22 indoor T8 fluorescent fixtures for the staircases and 4 90W floodlights for the entryways. Even though the fuse never pops, is it possible with all the wires and light sources that there is a lot of resistance causing the ballasts to be underpowered? Is this why only 1 one works on the buildings? I've checked with a voltmeter and the 120V go through the sockets.

Any help is appreciated!

nap 11-03-2010 08:56 PM

are all of these lights listed (the new 70 watt plus the 4 90 watt lights and the 22 fluorescent fixtures) on that one circuit? If so, and there is much of any length to the circuit you are probably getting one heck of a voltage drop on the circuit. That could cause a lot of problems.

and you are reading 120 volts in the socket? Where the lamp screws in?

BluesBpy721 11-03-2010 08:58 PM

Yes, the voltage in the actual socket reads 120V.

nap 11-03-2010 09:11 PM

hopefully marc (frenchelectrician) will catch this. He is the HID guru but until then, pretty sure the open circuit voltage is about 1/2 of what it should be.

Check the line voltage and make sure you connected the proper leads (if multi-tap ballast) of the ballast.

AllanJ 11-04-2010 06:58 AM

1. The fixtures may be el-cheapo.
2. The photocell unit (if non-mechanical i.e. not a contactor/relay) may be incompatible with the fixtures.
3. The fixture may have been meant to be hung as opposed to mounted on a wall or ceiling, the latter restricting the heat dissipation from the ballast.

As a metal halide or sodium or other typical non-incandescent lamp wamrs up, the voltage at the socket changes. The exact values are something that you just have to learn and know for each kind and wattage of lamp (if you wish to learn that). The open circuit voltage reading (no lamp in the socket) is not useful.

Quote:

I replaced 20 year old high pressure sodium fixtures with 70w metal halide ballasts a year ago.
You didn't use the wrong kind or size of lamp for the ballast did you?

alfred e neuman 11-04-2010 08:49 AM

Here's Advance ballast's troubleshooting guide, which includes the hookup data, and open circuit (socket w/o lamp installed) voltages.

http://www.wobblelight.com/downloads...ting-guide.pdf

BluesBpy721 11-04-2010 11:28 AM

Allan, I meant to say with fixtures...I guess all this time I kept my mind on the toasting ballasts I don't refer to them as fixtures anymore =P I'm pretty sure it's meant to be put on a wall. By the way, I've also had an electrician install one of these before we replaced almost the rest of them. I checked his setup to make sure everything is done the way the electrician did it (not much to it, anyway) and I did nothing different.

Here is the link to a similar wall pack: http://www.kingssupply.com/item342.htm/

It's not exactly what I have. I got mine from a Wilmar supply book, which is a little different...it is a multi-tap. However the 70W/120V holds true.

I guess I'll re-check the readings with the lightbulbs in.

J. V. 11-04-2010 11:39 AM

If it only takes 120 volts to operate a MH fixture, then why would you need a ballast. I think if you are reading 120 volts at the socket you have a voltage or a ballast tap problem. I am not certain as I have never measured the volts at the socket before, but it seems like the voltage should be much higher. Whats the ballast for if all you need is 120 volts?

BluesBpy721 11-04-2010 11:55 AM

Quote:

Originally Posted by J. V. (Post 528482)
If it only takes 120 volts to operate a MH fixture, then why would you need a ballast. I think if you are reading 120 volts at the socket you have a voltage or a ballast tap problem. I am not certain as I have never measured the volts at the socket before, but it seems like the voltage should be much higher. Whats the ballast for if all you need is 120 volts?

Yea, well I looked through the troubleshooting guide that alfred e neuman provided. I'll double-check the readings according to the guide later today. I'm actually of curious how or if the readings would change on a different circuit. The fact that there are so many feet in wires with all those light sources makes me wonder if I can even blame the fixtures anymore. I don't think they can be THAT defective. The death count is at 9, plus shortened life of light bulbs.

nap 11-04-2010 11:59 AM

Quote:

Originally Posted by J. V. (Post 528482)
If it only takes 120 volts to operate a MH fixture, then why would you need a ballast. I think if you are reading 120 volts at the socket you have a voltage or a ballast tap problem. I am not certain as I have never measured the volts at the socket before, but it seems like the voltage should be much higher. Whats the ballast for if all you need is 120 volts?

a ballast does more than convert voltage. There are some lamps that do need only 120 volts to operate (under 150 watt HPS for one example; see the link neuman posted) but a 50 watt MH should be over 200 volts so the open circuit voltage is definitely lower than design.

That is why I though OP might have used a tap for 208 or 240 volts in the fixture where he should have used a 120 volt tap.


so bluebpy, are they multi-tap ballasts? are you using proper tap?

BluesBpy721 11-04-2010 12:07 PM

Yea, these are quad-tapped. They're all hooked up on the 120V tap. Kinda hard to mess that up since the manufacturer capped the other 3 tap wires from the box...and they have labels =P

BluesBpy721 11-04-2010 03:12 PM

Okay, so I tested the fixtures according to the troubleshooting guide posted. I tested an apartment building that has 2 installed and working, and I also tested a single that is installed on the clubhouse that has much less on the circuit.

On the apartment building, the socket read at 184V

On the clubhouse, the socket read 192V then fell to 184V after a few seconds.

According to the voltage chart, it states the 70W M98 should be in the 205V - 290V range. So apparently I'm under by 20V. Are these ballasts just junk, then? The 120V taps are connected correctly, and the voltages coming in are around 122V.

nap 11-04-2010 03:45 PM

check the supply voltage while the lamp is starting and then after it has reached full brightness.

AllanJ 11-04-2010 06:46 PM

Quote:

Originally Posted by J. V. (Post 528482)
If it only takes 120 volts to operate a MH fixture, then why would you need a ballast. ?

The mercury halide light is designed to start with 120 volts. But as it warms up, the internal resistance goes down (opposite from an incandescent lamp whose resistance goes up as the filament heats up). In turn the current will get greater, great enough to blow out the lamp. The ballast restricts the current. By necessity this happens in the form of gradually dropping some of the voltage across itself as the current flowing through it increases, leaving fewer volts for the lamp. A happy medium is reached between voltage at the lamp socket and current flowing through the lamp (the specified values).

Meanwhile if we start the lamp off with just the voltage needed to draw the proper current at full brightness, it won't start.

nap 11-04-2010 07:22 PM

One thing I hadn't thought of but:

make sure you are using the proper lamp. It needs to match what the ballast says it is for.


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